The present invention relates generally to power transmission chains. The invention has particular application to power transmission chains of the roller chain variety, which are used primarily in automotive engine timing applications, but also can have automotive applications in the transfer of power from a torque converter to a transmission or in a transfer case of a four-wheel drive vehicle.
One type of chain is known as a "roller chain." A typical roller chain consists of alternate inner links and outer links. The inner links, which are also known as "bushing" links, consist of spaced inner plates with bushings tightly received in openings, or apertures, at each end of the inner plates. The outer links, which are also known as "pin" links or "guide" links, consist of spaced outer plates with pins tightly received in openings, or apertures, at each end of the outer plates. The bushings freely rotate about the pins to pivotally connect the outer links to the inner links in alternate arrangement. Rollers are provided on the bushings, and the roller chain is wrapped about a sprocket. The teeth of the sprocket are received between the laterally spaced plates and the longitudinally spaced rollers. Examples of roller chains are found in U.S. Pat. Nos. 4,196,617 and 5,226,856, which are both incorporated herein by reference.
Roller chain drives can include both "true roller" and rollerless design. The true roller design includes the described rollers mounted about the bushings. Rollerless chain or bushing chain contains bushings that directly contact the sprocket. Both types of roller chain are typically specified in industry as British Standard chain and American National Standards Institute (ANSI) chain.
A conventional roller chain drive includes an endless roller chain wrapped about at least two sprockets supported by shafts. Rotation of a driving sprocket causes power transmission through the chain and consequent movement of a driven sprocket. In an engine timing drive application, the driving sprocket is mounted on the engine crankshaft and the driven sprocket mounted on the camshaft. Various types of engine timing systems and configurations, which are suitable for roller chain assemblies, are shown in U.S. Pat. No. 5,427,580 which in incorporated herein by reference.
The present invention has particular application to chain assemblies in which the chains and sprockets are offset, or phased, to modify the impact noise spectrum and chordal action noise spectrum. In a typical phased chain system, a single strand chain assembly is divided into, or replaced by, two side-by-side chains that are phased or offset typically by one-half pitch.
Noise is generated with chain drives which can be caused, in part, by the impact sound generated by the collision of the chain and the sprocket at the onset of meshing. Many efforts have been made to decrease the overall noise level and pitch frequency noise distribution in automotive chain drives. Phasing the chain and sprocket relationship can reduce the number of chain rollers (or mass) impacting the sprocket during a given time increment. Similarly, phasing the chain and sprocket relationship can alter or phase the chordal action or articulation of the chain and sprocket. The present invention finds application in phased roller chain systems.
Phased chain systems as well as side-by-side non-phased systems are conventionally constructed with the two chains in a spaced-apart relationship. The spacing is provided between the two chains to assure that the chains do not contact one another during operation. In high speed automotive applications, significant movement occurs in the portions of each chain that span the longitudinal space between the driving and driven sprockets of each assembly. The separation between the two chains in the transverse direction is provided to prevent any contact between the two chain during such movement. Clearances between the chain and other structures are typically recommended in order to avoid contact from longitudinal or transverse movement of the chain during operation. The separation distance between the chains also contributes to the size or overall width of the chain package.
A portion of a roller chain having a single strand is illustrated in FIG. 1 and indicated generally by reference numeral 1 and each bushing link or "block" is indicated with reference numeral 3. A pin link 2 includes two plates 2.sub.1, 2.sub.1 integral and rigid connected by parallel pins 2.sub.2, 2.sub.2. A bushing link includes two plates 3.sub.1, 3.sub.1 respectively rigidly connected by parallel bushings 3.sub.2, 3.sub.2. Each bushing link 3 connects together two adjacent pin links and, conversely, each pin link connects together two adjacent bushing links.
In order to transmit heavy loads a double-strand chain as illustrated in FIG. 2 and indicated generally by reference numeral 10 has conventionally been used. This chain includes a series of pin links and bushing links or blocks connected one to the other. The pin links 12 have pins 12.sub.2 double the length of those of the chain in FIG. 1 and rigidly constrained to each other at their ends by means of outer plates 12.sub.2 double the length of those of the chain in FIG. 1 and rigidly connected to each other at their ends by means of outer plates 12.sub.1, 12.sub.1 and in an intermediate position by means of an intermediate plate 123. The bushing links 3 or "blocks" are conventional as in the example in FIG. 1; each includes two plates 3.sub.1, 3.sub.1 which rigidly constrain together two bushings 3.sub.2, 3.sub.2. Each pin link 12 is connected to the next one by means of two bushing links 3 located side by side on one side and the other of the intermediate plate 12.sub.3.
With the intention of reducing the noisiness of chains of the type illustrated in FIG. 2, though maintaining the strength thereof, use is also made of the system illustrated in FIG. 3 and indicated as a whole with reference numeral 20, which is composed of two roller chains 1, 1 like that shown in FIG. 1, arranged side by side and offset from each other by one-half pitch, i.e., with the axis of the pins and of the bushings of a chain offset by about 1/2 p with respect to those of the adjacent chain. Such a chain system is illustrated and described in U.S. Pat. No. 5,507,697 (1697). The '697 patent, though having given excellent results, nevertheless has the costly drawback that it is necessary to use two separate chains.